Linguistics aspects of speech and hearing of children who are wearing a cochlear implant (CI)

My research is about linguistics aspects of speech and hearing of children who are wearing a cochlear implant (CI).

A cochlear implant is a surgically implanted hearing device, which partly restores the hearing of deaf people. It applies to people having only a small number of functioning hair cells in the inner ear; this can involve both children and adults as well as people born deaf and people who acquired deafness at a later stage. Cochlear implantation has been performed for over thirty years; currently, over 300,000 individuals worldwide have received an implant and it is still becoming more widespread. What a CI technically does is to convert the acoustic signal, captured by a microphone carried on the outer ear, into an electric signal, bypassing the impaired hair cells.

We know from experimental research and also from the mechanics of the device that CI users have difficulty discriminating different frequencies, whereas time and intensity related contrasts are less problematic. In speech, frequency is a very important parameter: it carries the melody and accentuation of sentences. This is called prosody. Prosody has several crucial functions in speech, including the signaling of emotion, attitude, and the marking of important words.

Therefore, I investigate what prosodic contrasts users can or cannot hear and how this is reflected in their voice and in the way they produce prosody. Because different acoustic parameters, such as frequency, timing and intensity, can correlate in one prosodic phenomenon, implantees may be able to use these phenomena properly, but it is expected that the more they have to rely on frequency, the worse they perform. One way in which this can be tested is using vocoders.

These are simulations of CIs and have the advantage that the researcher can manipulate the settings and is not dependant on finding patients. Altogether, this research combines linguistic, medical and engineering disciplines.